The background of the invention will be set forth in two parts.
1. Field of the Invention
The present invention pertains to key operated cylinder locks, and more particularly to a pick-resistant cylinder lock.
2. Description of the Prior Art
A conventional lock utilizing tumbler pins including a cylinder having spring-loaded driver pins mounted therein for radial movement against key-activated tumbler or follower pins located in a core rotatably mounted in the cylinder.
Structural means is provided on the core for maintaining the pin holes in the core in axial alignment with the pin holes in the cylinder so that the driver pins are free to pass through the shear line between the core and the cylinder and into the cavities holding the follower pins. When a key designed for the lock is inserted into the key slot in the cylinder, the key engages the follower pins and moves them to a position where the abutting faces of the pins lie along the shear line, permitting the core to be rotated with respect to the cylinder by rotation of the key. This type of lock is very susceptible to being picked, or unlocked by unauthorized persons, by simply inserting a wire, or other elongated instrument, or instruments, which is manipulated in such a way as to simultaneously place a rotational force on the core of the lock while moving the follower pins, one at a time, into shear alignment with the peripheral surface of the core. The rotational force is necessary in order to capture a follower pin in its shear position while manipulating the other such pins of the lock, until all are in proper alignment to allow the core to be rotated.
Several cylinder locks have been developed in the past which are designed to resist the picking of same by unauthorized persons. One such lock is decribed in U.S. Pat. No. 2,596,720 in which the spring-loaded driver pins are provided with reduced diameter terminations abutting spacer disks or different diameter balls riding on an associated tumbler pin. In accordance with this design, each of the bores of the core are flanked by two relatively shallow recesses, or grooves, extending over a limited arch of the periphery of the barrel, or core, the depth of the grooves increasing toward the extremities remote from each bore to form an abutment. Accordingly, when an attempt is made to pick the lock, the core will begin to rotate as soon as the top of a disk lies flush with its periphery. The end terminations of the driver pins now ride in the grooves, and the maximum angle of rotation which will be reached after all the tumbler pins have been picked, is fixed by the abutments, which is insufficient to retract a latch controlled by the lock. It can thus be seen that each of the aligned tumbler bores must carry a plurality of relatively small components or elements, some of which must be relied on to carry extreme shear load in the case where an attempt is made to pick the lock.
Also, this type of lock can be picked by raising all the pins into the housing and then gradually lowering them, thus placing the wafers, or balls, in their normal position on the core. It can further be seen that this type of prior art design relies on luck or the law of averages that the small tipped pin, or the small ball, will be in position to lock into the depression.